This invention relates to a fuel injector for use in supplying fuel under pressure to a combustion space of an internal combustion engine. In particular, the invention relates to a fuel injector in which a characteristic of the fuel injector can be altered, in use.
In order to reduce the levels of noise and particulate emissions produced by an engine it is desirable to provide an arrangement whereby the injection characteristics of fuel delivered to the engine can be controlled. For example, it may be desirable to be able to adjust the spray pattern formed by the delivery of fuel by an injector or to adjust the rate of fuel injection. European Patent Application EP 0 713 004 A describes a fuel injector of the type in which the fuel injection characteristic can be varied, in use, by selecting different sets of fuel injector outlet openings provided in the fuel injector nozzle body. By controlling angular motion of a sleeve member, housed within the nozzle body, apertures formed in the sleeve are caused to align with selected ones of the outlet openings. Subsequent inward, axial movement of a valve member within the bore of the nozzle body causes fuel to be ejected from the selected outlet openings. Fuel injectors of this type do, however, have performance limitations.
Additionally, British Patent Application No. 9905231 describes a fuel injector including a nozzle body defining a bore within which an outwardly opening, outer valve member is slideable. Movement of the outer valve member in an outward direction causes fuel to be ejected from an upper group of outlet openings provided in the outer valve member. The outer valve member defines a blind bore within which an inner valve needle is slidable. Inward movement of the inner valve needle causes fuel injection through a lower group of outlet openings provided in the outer valve member. The fuel injection rate is controlled by means of an actuator arrangement which controls the downward force applied to the inner valve member. A fuel injector of this type does, however, suffer from the disadvantages of outwardly opening fuel injectors. For example, a poor spray characteristic is obtained as the outlet openings become exposed and, in addition, fuel leakage can occur from the outlet openings during undesirable stages of the fuel injection cycle.
It is an object of the present invention to provide an alternative fuel injector which enables the fuel injection characteristics to be varied, in use. It is a further object of the invention to provide a fuel injector which alleviates at least some of the disadvantages of fuel injectors of the outwardly opening type.
According to the present invention, there is provided a fuel injector comprising a nozzle body defining a bore within which an outer valve member is slidable, the outer valve member being engageable with a first seating to control fuel injection from a first outlet opening provided in a nozzle body, the outer valve member being provided with a through bore within which an inner valve member is slidable, the inner valve member being engageable with a second seating to control fuel injection through a second outlet opening provided in the nozzle body, the fuel injector further comprising first and second control chambers for fuel, whereby, in use, movement of the inner and outer valve members away from their respective seatings is controlled by controlling fuel pressure within the first and second control chambers so as to permit fuel delivery from a selected outlet opening.
The second seating may be defined by, or associated with, the outer valve member.
In a first fuel injecting position, the inner valve member only may be lifted away from the second seating and the outer valve member remains seated so that fuel injection occurs only through the second outlet opening. In a second fuel injecting position the outer valve member only may be lifted away from the first seating, a force due to movement of the outer valve member being transmitted to the inner valve member such that the inner valve member remains seated. Preferably, in the second fuel injecting position, fuel delivery through the second outlet opening is prevented. By providing first and second outlet openings of, for example, different size and shape, the fuel injection characteristics can therefore be varied by ejecting fuel from a selected outlet opening.
As inward movement of the outer valve member or the inner valve member away from their respective seatings permits fuel delivery through a selected outlet opening, the spray characteristic of fuel injected into the engine is improved. Furthermore, leakage from the outlet openings during undesirable stages of the fuel injection cycle is substantially avoided.
Conveniently, the outer valve member may include first and second valve parts, the first valve part being engageable with the first seating to control fuel flow through the first outlet opening and the second valve part being engageable with an additional seating. The first and second valve parts may together define a chamber for housing a sealing member and means may be provided for continuously biasing the sealing member against a sealing seating. The provision of the sealing member prevents any fuel leakage through the second outlet opening when the outer valve member is lifted away from the first seating and fuel delivery occurs through the first outlet opening.
In addition, the provision of the sealing member serves to prevent any fuel leakage through the first outlet opening when the inner valve member is lifted away from its seating and fuel delivery occurs through the second outlet opening.
The first and second valve parts of the outer valve member may be integrally formed to form a unitary body or may be separate parts which are connected together.
The first control chamber may be defined within the bore in the nozzle body, fuel pressure within the first control chamber serving to bias the outer valve member against the first seating. The outer valve member may include one or more thrust surfaces such that, in use, fuel pressure acting on the or each outer valve member thrust surface serves to urge the outer valve member inwardly against the action of fuel pressure within the first control chamber.
Fuel pressure within the second control chamber may serve to bias the inner valve member against the second seating. The inner valve member may include one or more thrust surfaces such that, in use, fuel pressure acting on the or each inner valve member thrust surface serves to urge the inner valve member inwardly against the action of fuel pressure within the second control chamber.
The fuel injector may include a piston member, a surface of which is exposed to fuel pressure within the second control chamber, in use, the piston member being arranged to transmit a force due to fuel pressure within the second control chamber to the inner valve member. Preferably, the effective diameter of the surface of the piston member exposed to fuel pressure within the second control chamber is greater than the diameter of the inner valve member.
The fuel injector may further comprise a first control valve arrangement for controlling fuel pressure within the first control chamber and a second control valve arrangement for controlling fuel pressure. within the second control chamber. Alternatively, the fuel injector may comprise a common control valve arrangement arranged to control fuel pressures within both the first and second control chamber.
The first and second outlet openings may be of different form to permit different fuel injection spray characteristics from the first and second outlet openings. For example, the first and second outlet openings may have a different size or each may be shaped to eject fuel with a different fuel spray angle.
The fuel injector may include a single first outlet opening or a group of first outlet openings from which fuel is injected into the engine at the first fuel injecting position. The fuel injector may include a single second outlet opening or a group of second outlet openings from which fuel is injected into the engine at the second fuel injecting position.